I got hit for the last time today. It was weird. I was making a PID controller for a constant voltage supply (30kV @ 1mA) (note that I have no idea how this supply works internally, but they wanted me to try and make an analog PID anyway). I had it up and running and was doing the initial P tweaking but I was getting zero voltage out of the thing, no matter what gain settings I tried (no I or D at this point). Then as I'm trimming one pot up (slowly) there was like this flash, not visible but felt, like static had hit both my forearms and face like a static discharge. The scope went out and I threw the power switch off.

I'm never doing anymore damn high voltage work for this company. No matter how many safety precautions I/we take something always happens. This was inside a box with the low voltage analog ckt well away from the HV load side, and somehow static must have built up somewhere. The supply must have gone unstable in the blink of an eye or something, but no way I'm [deleted by moderator] with a 30kV supply in a control loop that I don't know how it's going to react.

 

It isn't the High Voltage that is the problem, its understanding how it can travel.

And You should Definately understand the circuit before you build it or play with it.

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30kv? Pretty much everything conducts electricity at that point. How were you measuing the high side voltage, and what were the issolation methods, also how was the control signal fed back into the high voltage controller? You need some pretty severe issolation methods to keep voltages like that from getting to you, ambient air humidity or ANY condensation on a conductor can bypass an insulator and create a good current path for 1ma at those voltages. You'd at the very least want to be working in a very clean environment that has controlled humidity (as low as possible)

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The HV supply is a long skinny thing, with the HV output on one end and all the low voltage analog controls on the other. It's made by Ultravolt but I can't remember the part number, it's 30W 30kV. The A series I think. It's got +24VIN power, ground, current monitor output (0-5V for 0-1ma), +5V reference, programmable Vset pin (0-5V for 0-30kV) and a GND reference pin. It's meant to be controlled (voltage setpoint) by either a simple trimpot from the GND and 5V reference, or from a 0-5V DAC from a microcontroller. My job was to take the output of the current monitor pin and adjust the voltage programming pin to maintain a preset constant current through the load they will be attaching to this. When current falls it should increase voltage to compensate, or when current rises it would decrease voltage to compensate. The load can change very quickly so this is a 'fast' system. I had six 10KV 10Mohm resistors hooked up to the output as a dummy load on the far side of the HV enclosure this was in. Design had to be analog because this is in an insanely noisy environment (arc discharge nearby in the rxn chamber) and we've had lots of problems with microcontrollers resetting.

Anyway, the REAL problem is that no one at this company knows what they are doing with high voltage, and they are putting safety measures in place they think are adequate which apparently ARE NOT, and *I* have no business doing this kind of work. I was hired for microcontroller and electronics skills, and somehow they think because I know PID control systems that I can just apply it to a 30kV supply if they put a box around it.

Associated equipment was an isolated Fluke scopemeter, a 40kV 1000:1 HV probe and a 10:1 LV probe for the analog side (I've got test points everywhere so I could tune the loop and just clip on the test point and keep my hands away most of the time). This incident happened while I was adjusting a trimpot probably a foot or more away from any non-insulated wiring (basically only the resistor dummy load).

Apologies for the profanity earlier, I was quite angry in the immediate aftermath (still am) but I have cooled off a little. Fortunately I just interviewed with another company that has people who know what they're doing and doesn't work with anything over line voltage and who will probably give me a decent salary increase should I get an offer. I was going to stick around out of loyalty to my boss plus the fact he got me an early promotion to Engineer II (2-3 years at my company to get, I get it at 15 months when promotions are done in January). Should I get an offer I'm not sure I'll stick around for that.

Til then I am just telling my bosses I don't touch anything over 120. At least that won't jump out and get you.

ETA: I live near Houston, TX. And it's probably one of the most humid places in the state.

 

It's probably not much help - but HV jumps 1cm for every 10KV - in totally dry air. So if you have high humidity it's going to jump considerably more then the 3cm suggested by that.

Look on the bright side 1mA won't kill you.

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And 30kV doesn't hurt ---- for long.

Mike.

 

Dear Mr. Speakerguy79,

As your employer, we have reached a decision to terminate your employment due to your insubordinate actions regarding company mandated reasearch and development of high voltage projects. This action is immediate and any subsequent wages and accrued vacation time pay is to be forthcoming in the next payroll cycle. We regret your departure and wish you well with future business endeavors, despite your neurological medical claims received while on the job. At twelve o' clock noon, a security officer will escort you from the lab to your vehicle.

Regretfully,

Senior Management

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Not sure Why you would use a Load resistor of 60 Meg.

At 30KV, that 60M load trys to draw 1/2 Amp.

For 1mA you should have used a 30 Gig-ohm resistor.
I have resistors around that value and that 30KV voltage rating.

Maybe you should tell your boss to get some.

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Shouldn't that be ½mA?

Mike.

 

I certainly thought so?.

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YES, .5mA.

SORRY GUYS, I GOOFED.
Just got up and Not AWAKE YET.

My Apologies!
Gary

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Yep, I was trying to run the supply @ 50% Imax.

HiTech,

It would be nice if we got to cash out our vacation time. They ended that policy.